task.rb

class Task < ActiveRecord::Base
    attr_accessor :infile_file_name
    attr_accessor :infile_content_type
    attr_accessor :infile_file_size
    attr_accessor :infile_updated_at
    validates_presence_of :name
    has_attached_file :infile, :path => ":rails_root/public/system/:user_id/:id/inputs/:filename"
    belongs_to :user
end

tasks_controller.rb

#just a part of the file

    def create
        @user = User.find(params[:user_id])
        @task = Task.new(params[:task])
        @task.user_id = @user.id
        @task.status = 0
        if(@task.save)
            flash[:notice] = "Task " << @task.name << " has been successfuly registered"
            redirect_to :action => "index"
        else
            flash[:notice] = @task.errors
            redirect_to :action => "new"
        end
    end